This application is based on Application No. HEI 9-64358 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an image reading system suitable for reading bound documents such as books and magazines.
2. Description of the Related Art
Image readers such as copiers and the like are generally provided with a flat document table so as to copy the image of the sheet document under optimum image forming conditions. Accordingly, when a document such as a book is placed face downward on the document table, the center region in the viewing direction of the open faced document, i.e., the document surface, rises from the document table. The focus becomes defocused in this rising region so as to produce a reduction in image sharpness compared to other regions of the document surface. Japanese Laid-Open Patent No. 4-331562 discloses one method for correcting the aforesaid problem. This method measures the height distribution of the viewing surface via a range sensor, and corrects the reduced image sharpness via data processing in accordance with said measurement result. In image readers wherein a document is placed face upward, i.e., so-called book scanners, a method is used to measure the height distribution of the viewing surface and adjust the focus in conjunction with the progress of the scan in accordance with said measurement result. On the other hand, a proposed method of optimizing the sharpness of natural images utilizes image processing art to calculate the average intensity of the high frequency component in the edge regions in an image as an estimate standard of the sharpness of the entire image, and adjusts the edge highlight processing in accordance with said calculation result (23rd Image Engineering Conference, 1992, pp. 23-26).
In the aforesaid sharpness correction method based on the measured height distribution of the viewing surface, disadvantages in addition to the high cost of including a measurement mechanism arise insofar as the reading time is prolonged by said measurement process. Since the height distribution measurement is not further corrected when a document position is shifted after said measurement has occurred, an operator cannot be certain of the correction result for each reading, which becomes particularly troublesome when reading a plurality of pages.
It is unnecessary to measure the document height distribution in methods which estimate sharpness based on read image information. Since conventional methods of estimating sharpness use the entire image for said estimation, however, such methods are unsuitable for reading a viewing surface which has different degrees of sharpness at different locations. That is, such methods do not eliminate uneven sharpness via edge highlighting based on the average sharpness of an entire image. Furthermore, there is a tendency to excessive edge highlighting in text images having few characters.
An object of the present invention is to reduce the reading time and produce uniform image quality when reading open-faced documents.
These objects are attained by the image reading system of the present invention as described below.
The present invention provides an image reading system having an image sensing means to convert the image of an open-faced document to electronic signals in fine division in the viewing direction and a vertical direction perpendicular to said viewing direction, said image reading system comprising:
a counting means to count pixels of an image read by said image sensing means, the border pixels having a different binarized value than the binarized value of an adjacent pixel on one side in said vertical direction;
calculation means to calculate the difference of pixel value between each said border pixel and adjacent pixel on one side thereof; and
image correction means to correct pixel values in said pixel array in accordance with an image quality specified by the sum of said difference and the number of said border pixels of said pixel array in said vertical direction for each pixel position in said viewing direction.
The present invention further provides an image processing device having a means to detect the degree of sharpness of each of a plurality of regions in an image, and means to correct an image based on said degree of sharpness of each said region.
These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiments of the invention.